A conventional developing device has a developing chamber and a toner chamber positioned therebelow. The developing chamber accommodates therein a developing roller and a supply roller for supplying toner to the developing roller. The toner chamber accommodates therein a toner. In the toner chamber, an agitator is provided for lifting the toner in the toner chamber and for supplying the toner to the developing chamber. More specifically, the agitator includes a rotation shaft rotatably supported to the toner chamber, and a film member extending radially outwardly from the rotation shaft and slidably movable relative to an inner surface of the toner chamber. By the rotation of the rotation shaft, the film member is rotated so that the film member lifts and supplies the toner into the developing chamber through an opening formed at a boundary between the toiler chamber and the developing chamber.